The Fukushima Daiichi nuclear power plant (NPP) underwent a meltdown because of a loss of all power in the aftermath of a tsunami disaster following an extremely powerful earthquake in 2011. Although radioactive contamination around the Fukushima Daiichi NPP has already been cleaned up, and although the current radiation level is similar to that before the disaster, some areas with damaged reactors and melted nuclear fuel under the reactors at the NPP buildings still have strong radiation. Embedded systems with high radiation tolerance are necessary for robots able to remove the melted nuclear fuel and to decommission the reactors. Of course, current radiation-hardened VLSIs are useful for such purposes. Nevertheless, the total-ionizing-dose tolerances of such radiation-hardened VLSIs are limited to around 1 Mrad, which limits the radiation-hardened VLSI lifetime to 10 hr. Since such a short lifetimes of current radiation-hardened VLSIs is insufficient, a radiation-hardened VLSI with a higher total-ionizing-dose tolerance is being sought. To meet that demand, we have been developing radiation-hardened optically reconfigurable gate arrays comprising a silver-halide holographic memory, a laser, and an optically reconfigurable gate array VLSI. This paper presents estimation results of the entire total-ionizing-dose tolerance of a radiation-hardened optically reconfigurable gate array. Using a cobalt 60 gamma radiation source, the total-ionizing-dose tolerance of the optically reconfigurable gate array has been confirmed as at least 400 Mrad. That total-ionizing-dose tolerance is at least 400 times higher than the 1 Mrad total-ionizing-dose tolerance of a Vertex-5QV radiation-hardened field programmable gate array and other radiation hardened VLSIs.